Reddit Conversation Ads: Headline Limits and Thumbnail Size

Conversation Ads on Reddit are a placement, not a creative format. There are no image sizes of their own: you build the file to the specification of the ad type you picked, whether that is an Image Ad, a Video Ad, or a carousel.

Reddit creates the confusion itself. On its advertising site, Conversation Ad sits in the format table next to Image Ad and Video Ad, as if it were a separate ad type. In the Reddit Ads help center, the same Conversation is described differently: it is a placement, the second one after Feed, and you turn it on alongside the feed or instead of it.

The practical difference is that the placement does not change the file requirements, but it adds its own limits on top. Headlines are shorter in a thread, a separate thumbnail is required, and video does not start on its own.

Below are the parameters that change once your ad lands in the comments.

How the Conversation Placement Works

The placement is selected at the ad group level. The group settings give you three options: Feed, Conversation, or both.

Feed is the feed: the home page, Popular, and individual community feeds. Conversation is the discussion page, meaning a post with its comments open.

The ad position in a thread is fixed: between the post and the first comment.

People reach a thread two ways: from the Reddit feed and from search. The second group is the more interesting one for an advertiser, because those people might never have reached the Reddit feed at all.

If both placements are selected in the group, the same ad runs in the feed and in the thread. The file is one, but the display conditions differ: the headline limit is lower in a thread, the image displays more compactly, and video does not autoplay.

The rule for multi-placement: build the creative to the strictest limits among the ones you selected. The specific numbers are in the sections below.

Which Ad Types Are Available Here

The Conversation placement works with every ad type. You can put an Image Ad, a Video Ad, a carousel, or a free-form ad into a thread. There is no need to build a separate ad type for this placement.

There used to be restrictions. The placement did not work with the Video Views campaign objective, and gallery posts, text posts, and managed takeovers did not run in threads. Those restrictions are gone.

One old restriction still matters. Video in a thread does not autoplay and expands on click, so this placement is not used for a view-count task even when the objective is technically available. More on that in the video section.

Headline Limits

The headline is the only required text element of an ad, and this is where the Conversation placement limits you most.

• Feed: up to 300 characters.
• Conversation on desktop: up to 250 characters.
• Conversation on mobile: up to 100 characters.

Text beyond the limit gets cut off. The cut happens at display time: the ad saves in full in the interface, while a reader on a phone sees the first 100 characters in the thread.

Of the three numbers, the smallest one is the one that works. Most Reddit traffic is mobile, and with multi-placement the same ad goes to both the feed and the thread. The working headline length for Feed plus Conversation is 100 characters.

The headline has to make its point within the first 100 characters. If the business task requires a long headline, split it across separate ad groups: one group on Feed only with the long text, another on Conversation only with the short one. The placement is selected at the group level, so this adds no technical work.

Card Thumbnail

This is the key parameter of the placement and the only place where Conversation requires a separate file that your standard creative package may not include.

The thumbnail must be 400 × 300 px, aspect ratio 4:3, saved as a JPG up to 500 KB. It is not formally required — but in practice, you should always upload one.

A 400 × 300 thumbnail displays best in a thread. The standard 1200 × 628 image displays poorly in the compact block.

If you do not upload a thumbnail, Reddit takes the main ad image, the same 1200 × 628, and drops it into the compact slot. Shrinking a large image into a thumbnail hurts creative quality.

Resolution is not the only issue. The aspect ratios differ: 400 × 300 is 4:3, which is 1.33:1, while 1200 × 628 is 1.91:1. A thumbnail has to be fitted, and the composition of a feed creative does not carry over into a near-square slot. Text on the image and a logo near the edge do not survive that. Prepare a separate 4:3 frame.

If the ad has neither an image nor a video, a placeholder shows in the thread.

For weight and format there is one working answer: JPG up to 500 KB. It passes both the placement requirements and the general ad type requirements.

Images

The Conversation placement has no image size requirements of its own. The file is built to the specification of the ad type you selected, and that specification does not depend on the placement you turned on.

Ad specifications in a thread are the same as for a promoted post in the feed. Formats, file weight, aspect ratios, and recommended resolutions come from the Image Ad or carousel requirements.

What changes is the display. In the feed, the image takes the full width of the post. In a thread, the ad shows more compactly, and the 400 × 300 thumbnail from the previous section does the work. The same file reads differently across the two placements: an image with fine detail and captions loses its point in a compact block.

For the sizes specific to your ad type, see the separate articles on Image Ads and Carousel Ads. Those numbers do not change based on whether Conversation is on.

Video

In the feed, video autoplays. In a thread it does not: here it is click-to-play.

The mechanics are these. The reader first sees a thumbnail-sized preview, roughly the same as with an image. The clip expands and starts playing after a click.

This placement is not used for a view-count task. Every view requires a separate action from a person, so the video view rate in a thread comes out lower than in the feed with the same creative.

The 400 × 300 thumbnail is required. For video this is the same requirement as for an image. The thumbnail, not the first frame of the clip, decides whether a person clicks or scrolls past.

The point cannot live in the video alone. A 100-character headline plus the thumbnail have to work on their own, because part of the audience will not open the clip.

File requirements do not change. Formats, weight, duration, and aspect ratios come from the Video Ad specification; the placement does not override them.

The Video Views objective used to be unavailable with the Conversation placement, and that restriction has been lifted. It changes little in practice: click-to-play remains, and pairing Video Views with a thread produces a predictably expensive view.

Billing, Targeting, Reporting

Billing. The placement works with two bid types: CPM and CPC. Budgets are set daily or for the full campaign period.

Targeting. Every main Reddit targeting type is compatible with the Conversation placement: communities and interests, location, custom audiences (website retargeting, uploaded customer lists, Reddit engagement retargeting) and keywords. No audience setting is switched off when Conversation is enabled, so the group can be built on the same logic you use for the feed.

Reporting. Stats can be broken out by placement. In the dashboard this is done through Break Downs, where you select Placement. The breakdown is available for any campaign except app install metrics.

Turn the breakdown on right away if both placements are selected in the group. Without it, Feed and Conversation merge into one row, and there is no way to tell how much of the budget went into threads and what it produced. That data then decides whether to split the placements into separate groups with different headlines and thumbnails.

How to Preview Your Ad Before Launch

Ad Preview sits in the ad creation interface, below the list of saved ads.

Preview modes include Card, Classic and Conversation on mobile, plus Compact added on desktop.

Start with mobile Conversation. It shows the ad at the 100-character limit, the harshest version. If the headline reads there, it reads in the other modes as well.

What to check in the Conversation preview:

• the headline reaches its point instead of breaking mid-phrase;
• the block shows your 400 × 300 thumbnail, not a compressed main image;
• the subject and any text on the thumbnail are legible;
• the CTA button matches the action on the landing page.

Check before launch rather than after the first impressions. Headlines and thumbnails can be edited in an ad, but every edit sends it back through review.

Pre-Launch Checklist

Eight items, each one checked before you hit launch.

1. The headline fits 100 characters. If the group runs desktop only, the limit is 250, but for multi-placement and mobile impressions there is one working number.
2. The 400 × 300 thumbnail is uploaded manually. Automatic substitution of the main image produces a lower-quality compact block.
3. The thumbnail is a JPG under 500 KB.
4. The thumbnail composition is built for 4:3. A frame from a 1200 × 628 feed creative does not carry over into this slot.
5. Text and logo on the thumbnail are away from the edges.
6. The ad makes its point without opening the video, if the ad type is a Video Ad.
7. The CTA button matches the action on the landing page.
8. Placement breakdown is turned on in reporting, if the group has both Feed and Conversation selected.

The first five items cover almost every problem ads run into once they reach a thread: a cut-off headline and a blurry thumbnail built to the wrong ratio.